The present invention is directed to the field of electrical bus systems, particularly those of the type that carry large currents and thereby produce much excess heat. Electrical bus systems are commonly employed in telecommunications systems such as telephone and fiber optic systems using equipment where low voltages and high currents are required, preferably about 48 volts and 5000-10,000 amperes.
In a typical telecommunications system, alternating current (AC) is received from a supply, e.g., a utility, and passed through a rectifier to convert the current to direct current (DC). The direct current is used to supply the needs of the telecommunications equipment, e.g. telephone and fiber optic systems. As shown in FIG. 1, a telecommunications system 10 receives alternating current (AC) from a supply, e.g., a utility, and passes it through a rectifier 12 to convert the current to direct current (DC). This DC current is used to xe2x80x9cfloatxe2x80x9d one or more battery strings 16 to provide the load to the telecommunications system. The battery strings 16 are typically an array of conventional lead-acid or nickel-cadmium batteries. The batteries also provide an additional function of filtering out any signal noise or power spikes in the power supplied by the utility and thereby provide an electrical load at a consistent voltage and current.
Battery strings 16 also provide continuous service in the event of a power failure. A telecommunications office provides service to customers over a geographic area. It is therefore imperative that the equipment remain online even in the event of a power failure. In order to insure continuous operation, it is common to provide emergency backup systems, such as diesel-powered generators. However, a certain amount of startup time is required for generators, and it is important to insure against any power interruptions during this period. In the event of a power failure or other interruption of service, the battery strings 16 supply DC current to the telecommunications system 10, and thereby provide continuous, readily-available power.
Since the currents between the rectifier 12 and the battery strings 16 are very high, it is common to use an assembly of copper bus bars rather than stranded wire. As also shown in FIG. 1, the direct current is conducted between the battery strings 16 and the rectifier 12 along an assembly of bus bar laminations 14. In a typical bus work assembly, a number of bus bars are provided, each being copper plates, typically having widths of about eight inches. The bus bars are typically provided in laminations of as many as fourteen for each electrical polarity, and the laminations of each polarity are separated in order to insure safety.
For safety purposes, one common practice is to enclose the bus bar laminations 14 in a duct work. In this way, the bus bars are protected from external damage, e.g., from water leakage, and accidental short circuits that could result in injury to personnel and damage to equipment. Typically, the two bus bar polarities are retained within a safe proximity, so as to be enclosed within the same duct work assembly. The duct work relies on an air space to provide a degree of electrical isolation. Such duct work has traditionally been fabricated of either galvanized steel or aluminum.
During non-peak usage periods, a bus assembly may only operate at 10% of a maximum load capacity, a current of about 1000 amperes. However, during peak usage times, current loads can approach 100% capacity, about 10,000 amps. This creates a considerable amount of heat in the bus assembly, which reduces conductivity and can result in an undesirable reduction in available service and even damage to the system. This heat problem can be complicated by the duct work enclosure, since the metal ducts absorb the heat from the bus bars and thus retain a considerable amount of heat within the enclosure.
The difficulties and drawbacks of previous systems are overcome by the electrical bus system of the present invention in which first and second bus bar assemblies are provided for conducting electrical currents of respective first and second polarities. A bus duct enclosure is provided for enclosing the bus bar assemblies. The bus duct enclosure is adapted to provide a heat dissipative configuration. In one aspect of the invention, the bus duct enclosure can be formed of a substantially polycarbonate material, for providing convective heat dissipation from the bus bar assemblies.
As will be realized, the invention is capable of other and different embodiments and its several details are capable of modifications in various respects, all without departing from the invention. Accordingly, the drawing and description are to be regarded as illustrative and not restrictive.